1. Field of the Invention
This invention pertains to an apparatus for testing body fluid constituents. More particularly, this invention pertains to a sampler for use in collecting body fluids such as interstitial fluid.
2. Description of the Prior Art
In the prior art, there are numerous examples of apparatus for testing and determining the level of constituents in human blood. A great deal of attention has been directed to the development of techniques and apparatus for measuring blood glucose.
As noted in commonly assigned and co-pending U.S. patent application Ser. Nos. 08/321,305 and 08/136,304 (corresponding to PCT International Publication No. WO95/10223 published Apr. 20, 1995 on International Application No. PCT/US94/11580 and incorporated herein by reference), the determination of the level of a constituent of blood can be achieved by measuring the level of that constituent in other body fluids such as interstitial fluid. The aforementioned patent applications and international publication disclose a method and apparatus for a minimally invasive technique for collecting a sample of interstitial fluid through use of an extremely small needle which penetrates into the dermal layer of the skin in order to collect a low blood or blood-free sample of interstitial fluid. The collected interstitial fluid can then be analyzed for a determination of the level of constituents within the fluid. For example, the collected interstitial fluid can be analyzed for an amount of glucose with the determined amount being representative of the amount of glucose contained within the patient""s blood.
The aforementioned applications and international publication disclose the use of a ring (item 60 in FIG. 6 of the application) which surrounds the needle to create a pressure area on the patient""s skin. It is believed this leads to an increase in the amount of interstitial fluid being collected.
In the collection of interstitial fluid, it is desirable to increase the speed at which a sample is collected. In the absence of mechanical or other assistance, the rate at which interstitial fluid is collected through a small diameter tube or needle is very slow. Preferably, patients utilizing such equipment for home use will be provided with a system which collects interstitial fluid at a rapid pace to ensure that a patient does not remove the needle too early in its application. Also, it is important to provide for techniques to increase a volume of interstitial fluid being collected through a needle.
When collecting any body fluid through use of a needle, it is important that the needle be a disposable item in order to prevent re-use of the needle. Such re-use can result in the transmission of disease. Where the apparatus is to be used in a patient""s home by the patient, the apparatus should be simple to use and with the needle incorporated in a disposable item. Since the needle is incorporated in a disposable item, it is important that the disposable item be amenable to low-cost manufacture. Also, in order to test the interstitial fluid, the interstitial fluid collection mechanism must be coupled with an analytic mechanism for analyzing the collected fluid. Where such a device is to be used in home by low-skilled patients; it is important that the sampler and the analytic portion of the device be mutually configured to ensure that the sampler is coupled to the apparatus in a repeatable and reliable manner to minimize errors resulting from use of the apparatus by untrained patients.
According to a preferred embodiment of the present invention, a sampler is disclosed for use in a body fluid collection apparatus where the collection apparatus has a light source for generating a testing light and a light detector for detecting light. The light source and the detector are contained within the apparatus in a predetermined alignment to define a light path between the source and the detector. The apparatus further includes an opening of predetermined geometry to define an access to the light path. The sampler includes a main body having a handle and a sample end. The sample end has an external mating geometry which mates with the predetermined geometry of the opening of the apparatus. Therefore, the sample end can be inserted into the opening in a predetermined alignment such that the sampler may be repeatably inserted within the opening in the predetermined alignment with a sample location of the sample end positioned within the light path. A body fluid collection apparatus is carried on the sampler. The body fluid collection apparatus includes a needle sized to protrude beyond the housing. The needle protrudes a distance selected for the needle to penetrate into a body fluid-laden skin layer when the housing is urged against the skin layer by the user. An absorbent medium is carried on the sampler in fluid flow communication with the needle for body fluid to flow from the needle onto the medium. The medium is positioned at the sample location.